13-07-2016

Andrey Baryshev, Vyborg

Pointer testers such as 4353, 43101 and others were widespread at one time. The devices had built-in protection and made it possible to measure various electrical parameters, but they were cumbersome, and when measuring the capacitance of capacitors they were tied to the mains voltage. At the same time, the testers had good pointer measuring heads, which can be used in a design with much smaller dimensions and greater capabilities. So, using this head, a small desktop analog measuring device was made with a minimum number of controls. It allows you to measure, with sufficient accuracy for a radio amateur, the capacitance of non-polar capacitors (5 pF - 10 μF), the inductance of coils (from units of μH to 1 H), the capacitance of electrolytic capacitors (1 μF - 10,000 μF) and their ESR, and have it “at hand” fixed reference frequencies (10, 100. 1000 Hz, 10, 100, 1000 kHz) and, in addition, a built-in module can be added to it for quickly checking the performance of various low- and high-power transistors and determining the pinout of unknown transistors. Moreover, you can check the parameters of most elements without removing them from the circuit.

The modular design of the device allows you to use only the necessary functional units. Unnecessary modules can be easily excluded, and necessary ones can also be easily added if desired. The ability to preserve the “native” functions of the device - measuring voltages and currents - is also available. And, of course, the pointer measuring head can be any other (with a total deviation current of 50 ... 200 μA), this is not important. Next, diagrams and descriptions of individual functional “modules” of the device will be given, and then a block diagram of the entire device and a switching diagram of its individual components. All circuits have been tested in practice more than once and have shown stable and reliable operation, without complex settings or the use of any specific parts. If it is necessary to make a compact device for testing specific components and their parameters, each such circuit-module can be used separately.

Reference frequency generator

A widely used generator circuit based on digital elements was used, which, despite its simplicity, provides a set of necessary operating frequencies with good accuracy and stability, without requiring any settings.

The generator on the K561LA7 (or LE5) microcircuit is synchronized by a quartz resonator in the feedback circuit, which determines the frequency of the signal at its output (pins 10, 11), equal in this case to 1 MHz (Figure 1). The generator signal sequentially passes through several stages of frequency dividers by 10, assembled on K176IE4, CD4026 or any other microcircuits. The output of each stage produces a signal with a frequency ten times lower than the input frequency. Using any six-position switch, the signal from the generator or from any divider can be output. A circuit correctly assembled from serviceable parts works immediately and does not need adjustment. With capacitor C1, if desired, you can adjust the frequency within small limits. The circuit is powered by a voltage of 9 V.

Measuring module L, C

The cascade circuit for measuring the capacitance of non-polar capacitors and inductances is shown in Figure 2. The input signal is supplied directly from the output of the measurement range switch (SA1 in Figure 1). The generated rectangular pulse signal supplied to output “F” through the key transistor VT1 can be used to test or configure other devices. The output signal level can be adjusted with resistor R4. This signal is also supplied to the element being measured - a capacitor or inductance, connected, respectively, to terminals “C” or “L”, and switch SA2 is set to the appropriate position. To the exit “Umeas.” the measuring head is connected directly (possibly through an additional resistance; see below “Indication module”). Resistor R5 is used to set the measurement limits for inductances, and R6 - for capacitances. To calibrate the cascade, we connect a standard 0.1 µF capacitor to the “Cx” and “Common” terminals in the 1 kHz range (see the diagram in Figure 1) and use the trimming resistor R6 to set the device needle to the final scale division.

Then we connect capacitors, for example, with a capacity of 0.01, 0.022, 0.033, 0.047, 0.056, 0.068 uF and make the corresponding marks on the scale. After that, we calibrate the inductance scale in the same way, for which, in the same range of 1 kHz, we connect a model coil with an inductance of 10 mH to the “Lx” and “Common” terminals and use the trimming resistor R5 to set the arrow to the final division of the scale. However, the device can be calibrated at any other range (for example, at a frequency of 100 kHz or 100 Hz), connecting the corresponding capacitances and inductances as reference ones, according to the selected range.

Cascade supply voltage (Upit) is 9 V.

Electrolytic capacitor measurement module (+C and ESR)

The module is a microfaradometer in which the capacitance is determined indirectly by measuring the ripple voltage across resistor R3, which will change in inverse proportion to the capacitance of the periodically recharged capacitor. You can measure the capacitances of oxide (electrolytic) capacitors in the ranges of 10-100, 100-1000 and 1000-10000 μF.

The measuring unit for electrolytic capacitors is assembled on transistor T1 (Figure 3). The input (R1) is supplied with a signal directly from the output of the generator-divider (circuit in Figure 1), which can be connected in parallel to the previous module. We select resistor R1 depending on the type of transistor T1 used and the sensitivity of the measuring head used. Resistor R2 limits the collector current of the transistor in the event of a short circuit in the capacitor being tested. Unlike other modules, it requires a reduced stable power supply of 1.2 - 1.8 V; The stabilizer circuit for such a voltage will be shown below in Figure 6. It should be noted that when making measurements, the polarity of connecting the capacitor to the “+Cx” and “Common” terminals does not matter, and measurements can be performed without soldering the capacitors from the circuit. Before starting measurements with resistor R4, the arrow is set to zero (end of the scale).

Before starting measurements (in the absence of a measured capacitor “+Cx”), resistor R4 sets the arrow to zero (the final scale division). Calibration of the “+Cx” scale can be performed on any range. For example, we move switch SA1 to the position corresponding to the frequency of 1 kHz. Using R4, set the device pointer to “0” (end of the scale) and, connecting standard capacitors with a capacity of 10, 22, 33, 47, 68 and 100 μF to the “+Cx” and “Common” terminals, make the corresponding marks on the scale. After this, on other ranges (10 Hz and 100 Hz), the same marks will correspond to capacitances with ratings 10 and 100 times larger, that is, from 100 to 1000 μF (100, 220, 330, 470, 680 μF) and from 1000 up to 10000 µF, respectively. Tantalum oxide-semiconductor capacitors that have the most stable parameters over time, for example, types K53-1 or K53-6A, can be used as exemplary ones.

The ESR measurement unit contains a separate 100 kHz oscillator, assembled on a 561LA7 (LE5) chip using the same circuit as the main oscillator in Figure 1. No special stability is required here, and the frequency can be any from 80 to 120 kHz. The current flowing through winding I of the transformer (wound on a ferrite ring with a diameter of 15 - 20 mm) depends on the value of the series equivalent resistance of the capacitor connected to the terminals. The brand of ferrite does not matter, but perhaps the number of turns of the primary winding will need to be adjusted. Therefore, it is better to wind winding II first, and the primary winding on top of it. The rectified DC voltage after the VD5 diode is supplied to the measuring head (display module in Figure 4). Diodes VD3, VD4 limit possible voltage surges to protect the pointer head from overload. Here, the polarity of the capacitor connection is also not important, and measurements can be carried out directly in the circuit.

The measurement limits can be changed over a wide range using tuning resistor R5 - from tenths of an ohm to several ohms. But at the same time, you should take into account the influence of the resistance of the wires from the “ESR” and “Common” terminals. They should be as short as possible and have a large cross-section. If this module is located close to another source of pulse signals (for example, next to the generator Figure 1), the generation of the node on the chip may be disrupted. Therefore, it is better to assemble the “ESR” measurement unit on a separate small board and place it in a screen (for example, made of tin) connected to a common wire.

To calibrate the “ESR” scale, connect resistors with a resistance of 0.1, 0.2, 0.5, 1, 2. 3 Ohms to the “ESR” and “Common” terminals and make the corresponding marks on the scale. The sensitivity of the device can be adjusted by changing the resistance of the tuning resistor R5.

The ESR meter is powered, just like the rest of the module circuits, with a voltage of 9 V.

Device module connection diagram

As can be seen from Figure 4, connecting all the “modules” is not difficult. The display module includes a measuring head, shunted with a capacitor (100 ... 470 μF) to eliminate the “jitter” of the needle when measuring in ranges with a low frequency of the master oscillator. Depending on the sensitivity of the measuring head, additional resistance may be required.

It should be kept in mind that the “Common” terminal in Figure 2 (measurement module “C” and “L”) is not the common wire of the circuit (!) and requires a separate socket.

Add-ons

If necessary, the composite transistor T1 (circuit in Figure 3) can be replaced with a unit of two transistors of lower power, and in a 1.4 V power supply you can use a simple stabilizer on one transistor. How to do this is shown in Figures 5 and 6. The function of the zener diode here is performed by silicon diodes VD1-VD3 with a total forward voltage drop of about 1.5 V. The diodes, unlike the zener diode, must be turned on in the forward direction.

If desired, you can supplement the device with a module for quickly checking transistors. It can be used to test any bipolar transistors, as well as low- and medium-power field-effect transistors. Moreover, bipolar transistors and, in some cases, field-effect transistors can be checked without removing them from the circuit. The circuit presented in Figure 7 is a combination of a multivibrator and a trigger, where instead of load resistors, transistors with identical parameters, but of opposite structure (VT2, VT3) are included in the collector circuits of the multivibrator transistors. Resistors R6, R7 set the required bias voltage for the operating point of the transistor being tested, and R5 limits the current through the LEDs and determines the brightness of their glow.

Depending on the type of LEDs used, you may have to select resistance R5, focusing on the optimal brightness of their glow, or install an additional quenching resistor in the 9 V power circuit. It should be noted that this circuit works with a supply voltage starting from 2 V. When nothing is connected to terminals “E”, “B”, “K”, both LEDs are blinking. The blinking frequency can be adjusted by changing the capacitance of capacitors C1 and C2. When a working transistor is connected to the terminals, one of the LEDs will go out, depending on its conductivity type - p-n-p or n-p-n. If the transistor is faulty, both LEDs will blink (internal open) or both will go out (short). In addition to the terminals “E”, “B”, “K” on the device itself (terminal block, “fragment” of a socket for microcircuits, etc.), in parallel with them, you can remove the corresponding probes from the housing on the wires to test transistors on the boards. When testing field-effect transistors, terminals “E”, “B”, “K” correspond to terminals “I”, “Z”, “C”.

It should be noted that it is still better to check field-effect transistors or very powerful bipolar transistors by removing them from the board.

When measuring the values ​​of any elements directly on the board, be sure to turn off the power to the circuit in which the measurements are being made!

The device takes up little space, fitting into a 140×110×40 mm housing (see photo on the right at the beginning of the article) and allows you to test almost all the main types of radio components most often used in practice with sufficient accuracy for radio amateurs. The device has been in use for several years without any complaints.

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Is it possible to check a field-effect transistor with a multimeter? Checking transistors without desoldering from the circuit with a multimeter

A device for testing any transistors

This is another article dedicated to a novice radio amateur. Checking the functionality of transistors is perhaps the most important thing, since it is a non-working transistor that causes the failure of the entire circuit. Most often, novice electronics enthusiasts have problems checking field-effect transistors, and if you don’t even have a multimeter at hand, then it is very difficult to check the transistor for functionality. The proposed device allows you to check any transistor, regardless of type and conductivity, in a few seconds.

The device is very simple and consists of three components. The main part is the transformer. You can take any small-sized transformer from switching power supplies as a basis. The transformer consists of two windings. The primary winding consists of 24 turns with a tap from the middle, the wire is from 0.2 to 0.8 mm.

The secondary winding consists of 15 turns of wire of the same diameter as the primary. Both windings wind in the same direction.

The LED is connected to the secondary winding through a 100 ohm limiting resistor, the power of the resistor is not important, nor is the polarity of the LED, since an alternating voltage is generated at the output of the transformer. There is also a special attachment into which the transistor is inserted, observing the pinout. For direct bipolar transistors (type KT 818, KT 814, KT 816, KT 3107, etc.), the base goes through a base 100 ohm resistor to one of the terminals (left or right terminal) of the transformer, the middle point of the transformer (tap) is connected to the power plus, the emitter of the transistor is connected to the power minus, and the collector to the free terminal of the primary winding of the transformer.

For reverse conduction bipolar transistors, you just need to change the power polarity. The same is true with field-effect transistors, it is just important not to confuse the pinout of the transistor. If after applying power the LED starts to light up, then the transistor is working, but if not, then throw it in the trash, since the device provides 100% accuracy in checking the transistor. These connections need to be made only once, during assembly of the device, the attachment can significantly reduce the time of checking the transistor; you just need to insert the transistor into it and apply power. The device, in theory, is a simple blocking generator. The power supply is 3.7 - 6 volts, just one lithium-ion battery from a mobile phone is perfect, but you need to remove the board from the battery in advance, since this board turns off the power; current consumption exceeds 800 mA, and our circuit can consume such current in peaks. The finished device turns out to be quite compact; you can place it in a compact plastic case, for example, from tick-tock candies, and you will have a pocket device for testing transistors for all occasions.

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DIAGNOSTICS AND REPAIR OF ELECTRONICS WITHOUT SCHEMATICS

In the life of every home craftsman who knows how to hold a soldering iron and use a multimeter, there comes a time when some complex electronic equipment breaks down and he is faced with a choice: to send it to a service center for repairs or to try to repair it himself. In this article we will look at techniques that can help him with this. So, your equipment is broken, for example an LCD TV, where should you start repairing it? All craftsmen know that it is necessary to begin repairs not with measurements, or even immediately resolder the part that aroused suspicion of something, but with an external examination. This includes not only inspecting the appearance of the TV circuit boards, removing its cover, looking for burnt radio components, and listening to hear a high-frequency squeak or click. We connect the device to the network To begin with, you just need to turn on the TV to the network and see: how it behaves after turning it on, whether it responds to the power button, or the standby mode LED is blinking, or the image appears for a few seconds and disappears, or there is an image but there is no sound, or vice versa. Based on all these signs, you can obtain information from which you can build upon for further repairs. For example, by blinking an LED at a certain frequency, you can set a fault code, self-testing of the TV. TV error codes by LED blinking After the signs have been established, you should look for a schematic diagram of the device, or better yet, if a Service manual for the device has been issued, documentation with a diagram and a list of parts, on special websites dedicated to electronics repair. It will also not be amiss in the future to enter the full name of the model into a search engine, with a brief description of the breakdown, conveying its meaning in a few words. Service manual True, sometimes it is better to search for a diagram by the device chassis, or the name of the board, for example a TV power supply. But what if you still couldn’t find the circuit, and you are not familiar with the circuitry of this device? Block diagram of LCD TV In this case, you can try to ask for help on specialized forums for repairing equipment, after conducting preliminary diagnostics yourself, in order to collect information from which the technicians helping you can build on. What stages does this preliminary diagnosis include? First, you must make sure that power is supplied to the board if the device does not show any signs of life at all. This may seem trivial, but it wouldn’t hurt to test the power cord for integrity using the audio test mode. Read here how to use a regular multimeter. Tester in audio mode Then the fuse is tested in the same multimeter mode. If everything is fine here, we should measure the voltage at the power connectors going to the TV control board. Typically, the supply voltages present on the connector pins are labeled next to the connector on the board. TV control board power connector So, we measured and there is no voltage at the connector - this indicates that the circuit is not functioning correctly, and we need to look for the reason for this. The most common cause of breakdowns found in LCD TVs are banal electrolytic capacitors, with high ESR, equivalent series resistance. Read more about ESR here. Capacitor ESR Table At the beginning of the article, I wrote about a squeak that you may hear, and so its manifestation, in particular, is a consequence of the overestimated ESR of small-value capacitors located in the standby voltage circuits. To identify such capacitors, you need a special device, an ESR meter, or a transistor tester, although in the latter case, the capacitors will have to be unsoldered for measurement. I posted a photo of my ESR meter that allows me to measure this parameter without soldering below. My ESR meter What to do if such devices are not available, and suspicion falls on these capacitors? Then you will need to consult on repair forums and clarify in which node, which part of the board, the capacitors should be replaced with ones that are known to work, and only new (!) capacitors from a radio store can be considered as such, because used ones have this parameter, ESR may also be off the charts or already on the verge. Photo - swollen capacitor The fact that you could remove them from a device that previously worked does not matter in this case, since this parameter is important only for working in high-frequency circuits; accordingly, earlier, in low-frequency circuits, in another device, this capacitor could function perfectly, but have an ESR parameter that is very high. The work is greatly facilitated by the fact that high-value capacitors have a notch in their upper part, along which, if they become unusable, they are simply opened, or a swelling forms, a characteristic sign of their unsuitability for anyone, even a novice master. Multimeter in Ohmmeter mode If you see blackened resistors, you will need to test them with a multimeter in ohmmeter mode. First, you should select the 2 MOhm mode; if the screen shows values ​​that differ from unity, or the measurement limit is exceeded, we should accordingly reduce the measurement limit on the multimeter to establish its more accurate value. If there is one on the screen, then most likely such a resistor is broken and should be replaced. Color coding of resistors If it is possible to read its denomination by marking it with colored rings applied to its body, it’s good, otherwise you can’t do without a diagram. If the circuit is available, then you need to look at its designation and set its rating and power. If the resistor is precision, its (precise) value can be set by connecting two ordinary resistors in series, a larger and a smaller value, the first we set the value roughly, the last we adjust the accuracy, and their total resistance will add up. Transistors are different in the photo Transistors, diodes and microcircuits: it is not always possible to determine a malfunction with them by appearance. You will need to measure with a multimeter in audio testing mode. If the resistance of any of the legs, relative to some other leg, of one device, is zero, or close to it, in the range from zero to 20-30 Ohms, most likely such a part must be replaced. If it is a bipolar transistor, you need to call its p-n junctions in accordance with the pinout. Most often, such a check is enough to consider the transistor to be working. A better method is described here. For diodes, we also cause a p-n junction, in the forward direction, there should be numbers of the order of 500-700 when measured, in the reverse direction one. The exception is Schottky diodes, they have a lower voltage drop, and when calling in the forward direction, the screen will show numbers in the range of 150-200, and in the reverse direction it will also be one. Mosfets and field-effect transistors cannot be checked with a conventional multimeter without soldering; you often have to consider them conditionally working if their terminals do not short-circuit with each other, or have low resistance. Mosfet in SMD and regular housing It should be taken into account that mosfets have a built-in diode between the Drain and the Source, and when dialing, the readings will be 600-1600. But there is one nuance here: if, for example, you ring the mosfets on the motherboard and hear a beep at the first touch, do not rush to write the mosfets into the broken one. Its circuits contain electrolytic filter capacitors, which, when charging begins, are known to behave for some time as if the circuit were short-circuited. Mosfets on PC motherboard This is what our multimeter shows, in audible dialing mode, with a squeak for the first 2-3 seconds, and then increasing numbers will appear on the screen, and the unit will be set as the capacitors charge. By the way, for the same reason, in order to save the diodes of the diode bridge, a thermistor is installed in switching power supplies that limits the charging currents of electrolytic capacitors at the moment of switching on, through the diode bridge. Diode assemblies on the diagram Many novice repairmen I know who seek remote advice on VKontakte are shocked - you tell them to ring the diode, they ring it and immediately say: it’s broken. Here, as a standard, an explanation always begins that you need to either lift, unsolder one leg of the diode, and repeat the measurement, or analyze the circuit and board for the presence of parallel-connected parts in low resistance. These are often the secondary windings of a pulse transformer, which are connected parallel to the terminals of the diode assembly, or in other words, a dual diode. Parallel and series connection of resistors Here it is best to remember once, the rule of such connections: When two or more parts are connected in series, their total resistance will be greater than the greater resistance of each individually. And with a parallel connection, the resistance will be less than the smaller of each part. Accordingly, our transformer winding, which has a resistance of 20-30 Ohms at best, by shunting, imitates for us a “broken” diode assembly. Of course, unfortunately, it is impossible to reveal all the nuances of repairs in one article. For preliminary diagnosis of most breakdowns, as it turned out, a conventional multimeter used in the voltmeter, ohmmeter, and audio test modes is sufficient. Often, if you have experience, in the event of a simple breakdown and subsequent replacement of parts, the repair is completed, even without a diagram, carried out by the so-called “scientific poking method”. Which, of course, is not entirely correct, but as practice shows, it works, and, fortunately, not at all as shown in the picture above). Successful repairs to everyone, especially for the Radio Circuits website - AKV. Repair forum Discuss the article DIAGNOSTICS AND REPAIR OF ELECTRONICS WITHOUT DIAGRAMS

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how to test a transistor using a multimeter

In this article, we will tell you how to test a transistor with a multimeter. Surely many of you are well aware that most multimeters have a special socket in their arsenal, but not in every situation the use of the socket is convenient and optimal. So, in order to select several elements that have the same gain, the use of a socket is quite justified, and to determine the operability of the transistor, it is quite enough to use a tester.

about the transistor

Let's remember that regardless of whether we are checking a transistor with forward or reverse conduction, they have two p-n junctions. Any of these transitions can be compared to a diode. Based on this, we can confidently say that a transistor is a pair of diodes connected in parallel, and the place where they are connected is the base.

Thus, it turns out that for one of the diodes the leads will represent the base and collector, and for the second diode the leads will represent the base and emitter, or vice versa. Based on what was written above, our task comes down to checking the drop voltage on a semiconductor device, or checking its resistance. If the diodes are operational, then the element being tested is working. First, let’s consider a transistor with reverse conductivity, that is, having an N-P-N conductivity structure. On electrical circuits of various devices, the structure of the transistor is determined using an arrow that indicates the emitter junction. So if the arrow points to the base, then we are dealing with a forward conduction transistor having a p-n-p structure, and if on the contrary, then it is a reverse conduction transistor having an n-p-n structure.

To open a direct conduction transistor, you need to apply a negative voltage to the base. To do this, take a multimeter, turn it on, and then select the continuity measurement mode, usually indicated by a symbolic image of a diode.

In this mode, the device displays the voltage drop in mV. Thanks to this, we can identify a silicon or germanium diode or transistor. If the voltage drop is in the range of 200-400 mV, then we have a germanium semiconductor, and if it is 500-700, a silicon one.

Checking the functionality of the transistor

We connect the positive probe (red) to the base of the transistor, connect the other probe (black - minus) to the collector terminal and take a measurement

Then we connect the negative probe to the emitter terminal and measure.

If the transistor junctions are not broken, then the voltage drop across the collector and emitter junction should be on the border from 200 to 700 mV.

Now let's make a reverse measurement of the collector and emitter junction. To do this, we take and connect the black probe to the base, and connect the red one in turn to the emitter and collector, taking measurements.

During the measurement, the number “1” will be displayed on the device screen, which in turn means that in the measurement mode we have chosen, there is no voltage drop. In the same way, you can check an element that is located on an electronic board from any device, and in many cases you can do without desoldering it from the board. There are cases when soldered elements in a circuit are greatly influenced by low-resistance resistors. But such schematic solutions are very rare. In such cases, when measuring the reverse collector and emitter junction, the values ​​​​on the device will be low, and then you need to unsolder the element from the printed circuit board. The method for checking the functionality of an element with reverse conductivity (P-N-P junction) is exactly the same, only the negative probe of the measuring device is connected to the base of the element.

Signs of a faulty transistor

Now we know how to determine a working transistor, but how to check a transistor with a multimeter and find out that it is not working? Here, too, everything is quite easy and simple. The first malfunction of the element is expressed in the absence of a voltage drop or in an infinitely large resistance of the direct and reverse p-n junction. That is, when dialing, the device shows “1”. This means that the measured transition is open and the element is not working. Another malfunction of the element is expressed in the presence of a large voltage drop across the semiconductor (the device usually beeps), or near zero resistance values ​​of the forward and reverse p-n junctions. In this case, the internal structure of the element is broken (short-circuited), and it is not working.

Determining the pinout of a transistor

Now let's learn how to determine where the base, emitter and collector are located on a transistor. First of all, they begin to look for the base of the element. To do this, turn the multimeter into dialing mode. We attach the positive probe to the left leg, and with the negative probe we sequentially measure on the middle and right leg.

The multimeter showed us “1” between the left and middle legs, and between the left and right legs the readings were 555 mV.

So far, these measurements do not allow us to draw any conclusions. Let's move forward. We fix the positive probe on the middle leg, and sequentially measure with the minus probe on the left and right legs.

The toaster showed a value of "1" between the left and middle legs, and 551 mV between the middle and right legs.

These measurements also do not make it possible to draw a conclusion and determine the base. Let's move on. We fix the plus probe on the right leg, and with the minus probe we fix the middle and left leg in turn, while taking measurements.

During the measurement, we see that the voltage drop between the right and middle legs is equal to one, and between the right and left legs is also equal to one (infinity). Thus, we have found the base of the transistor, and it is located on the right leg.

Now we just need to determine which leg is the collector and which leg is the emitter. To do this, the device should be switched to measuring resistance of 200 kOhm. We measure on the middle and left leg, for which we will fix the probe with a minus on the right leg (base), and we will fix the positive one in turn on the middle and left legs, while measuring the resistance.

Having received the measurements, we see that on the left leg R = 121.0 kOhm, and on the middle leg R = 116.4 kOhm. You should remember once and for all, if you subsequently check and find the emitter and collector, that the resistance of the collector junction is in all cases less than the resistance of the emitter.

Let's summarize our measurements:

1. The element we are measuring has a p-n-p structure.
2. The base leg is located on the right.
3. The collector leg is located in the middle.
4. The emitter leg is on the left.

Try and determine the performance of semiconductor elements, it’s very easy!

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Testing a Bipolar Transistor - Electronics Basics

Greetings to all electronics lovers, and today, in continuation of the topic of using a digital multimeter, I would like to tell you how to test a bipolar transistor using a multimeter.

A bipolar transistor is a semiconductor device that is designed to amplify signals. The transistor can also operate in switching mode.

The transistor consists of two p-n junctions, with one of the conduction regions being common. The middle overall region of conduction is called the base, the outermost regions the emitter and the collector. As a result, n-p-n and p-n-p transistors are separated.

So, schematically a bipolar transistor can be represented as follows.

Figure 1. Schematic representation of a transistor a) n-p-n structure; b) p-n-p structures.

To simplify the understanding of the issue, p-n junctions can be represented as two diodes connected to each other by electrodes of the same name (depending on the type of transistor).

Figure 2. Representation of an n-p-n transistor structure in the form of an equivalent of two diodes connected with anodes to each other.

Figure 3. Representation of a p-n-p transistor structure in the form of an equivalent of two diodes connected with cathodes facing each other.

Of course, for a better understanding, it is advisable to study how the pn junction works, or better yet, how the transistor works as a whole. Here I will only say that in order for current to flow through the p-n junction, it must be turned on in the forward direction, that is, a minus must be applied to the n-region (for a diode this is the cathode), and a minus to the p-region (anode).

I showed this to you in the video for the article “How to use a multimeter” when checking a semiconductor diode.

Since we presented the transistor in the form of two diodes, then, therefore, to check it you just need to check the serviceability of these same “virtual” diodes.

So, let's start checking the transistor of the n-p-n structure. Thus, the base of the transistor corresponds to the p-region, the collector and emitter to the n-regions. First, let's put the multimeter in diode testing mode.

In this mode, the multimeter will show the voltage drop across the pn junction in millivolts. The voltage drop across the pn junction for silicon elements should be 0.6 volts, and for germanium elements - 0.2-0.3 volts.

First, let's turn on the p-n junctions of the transistor in the forward direction; to do this, connect the red (plus) multimeter probe to the base of the transistor, and connect the black (minus) multimeter probe to the emitter. In this case, the indicator should display the value of the voltage drop at the base-emitter junction.

It should be noted here that the voltage drop across the B-K junction will always be less than the voltage drop across the B-E junction. This can be explained by the lower resistance of the B-K junction compared to the B-E junction, which is a consequence of the fact that the collector conduction region has a larger area compared to the emitter.

Using this feature, you can independently determine the pinout of the transistor, in the absence of a reference book.

So, half the job is done, if the transitions are working properly, then you will see the voltage drop values ​​​​across them.

Now you need to turn on the p-n junctions in the opposite direction, and the multimeter should show “1”, which corresponds to infinity.

We connect the black probe to the base of the transistor, the red one to the emitter, and the multimeter should show “1”.

Now we turn on the B-K transition in the opposite direction, the result should be similar.

The last check remains - the emitter-collector transition. We connect the red probe of the multimeter to the emitter, the black one to the collector, if the transitions are not broken, then the tester should show “1”.

We change the polarity (red-collector, black-emitter), the result is “1”.

If, as a result of the test, you find that this method does not comply with this method, this means that the transistor is faulty.

This technique is suitable for testing only bipolar transistors. Before testing, make sure that the transistor is not field effect or compound. Many people use the method outlined above to try to check precisely composite transistors, confusing them with bipolar ones (after all, the type of transistor can be incorrectly identified by the markings), which is not the right solution. You can correctly find out the type of transistor only from a reference book.

If there is no diode test mode in your multimeter, you can check the transistor by switching the multimeter to the resistance measurement mode in the “2000” range. In this case, the testing method remains unchanged, except that the multimeter will show the resistance of the p-n junctions.

And now, by tradition, an explanatory and complementary video on checking the transistor:

www.sxemotehnika.ru

How to check a transistor, diode, capacitor, resistor, etc.

How to check the functionality of radio components

Failures in the operation of many circuits sometimes occur not only due to errors in the circuit itself, but also due to a burnt or simply defective radio component somewhere.

When asked how to check the functionality of a radio component, a device that probably every radio amateur has - a multimeter - will help us in many ways.

The multimeter allows you to determine voltage, current, capacitance, resistance, and much more.

How to test a resistor

The constant resistor is checked with a multimeter turned on in ohmmeter mode. The result obtained must be compared with the nominal resistance value indicated on the resistor body and on the circuit diagram.

When checking trimmer and variable resistors, you first need to check the resistance value by measuring it between the outermost (according to the diagram) terminals, and then make sure that the contact between the conductive layer and the slider is reliable. To do this, you need to connect an ohmmeter to the middle terminal and alternately to each of the outer terminals. When the resistor axis is rotated to its extreme positions, the change in resistance of the variable resistor of group “A” (linear dependence on the angle of rotation of the axis or position of the slider) will be smooth, and the change in the resistance of the variable resistor of group “B” or “C” (logarithmic dependence) is nonlinear. Variable (tuning) resistors are characterized by three malfunctions: violation of contact between the motor and the conductive layer; mechanical wear of the conductive layer with partial breakdown of contact and an upward change in the resistor resistance value; burnout of the conductive layer, as a rule, at one of the outer terminals. Some variable resistors have a dual design. In this case, each resistor is tested separately. Variable resistors used in volume controls sometimes have taps from the conductive layer intended for connecting loudness circuits. To check the presence of contact between the tap and the conductive layer, an ohmmeter is connected to the tap and any of the outer terminals. If the device shows some part of the total resistance, then there is contact between the tap and the conductive layer. Photoresistors are tested similarly to conventional resistors, but they will have two resistance values. One before illumination is the dark resistance (indicated in reference books), the second is when illuminated by any lamp (it will be 10... 150 times less than the dark resistance).

How to check capacitors

The simplest way to check the serviceability of a capacitor is an external inspection, during which mechanical damage is detected, for example, deformation of the housing due to overheating caused by a large leakage current. If no defects are noticed during an external inspection, an electrical test is carried out. An ohmmeter can easily determine one type of malfunction - an internal short circuit (breakdown). The situation is more complicated with other types of capacitor failure: internal break, high leakage current and partial loss of capacitance. The cause of the last type of malfunction in electrolytic capacitors is drying out of the electrolyte. Many digital testers provide capacitance measurements in the range of 2000 pF to 2000 µF. In most cases this is enough. It should be noted that electrolytic capacitors have a fairly large spread in the permissible deviation from the nominal capacitance value. For some types of capacitors it reaches - 20%, + 80%, that is, if the capacitor rating is 10 μF, then the actual value of its capacitance can be from 8 to 18 μF.

If you do not have a capacitance meter, the capacitor can be checked in other ways. Large capacitance capacitors (1 µF and above) are checked with an ohmmeter. In this case, the parts are soldered off from the capacitor if it is in the circuit and discharged. The device is installed to measure high resistances. Electrolytic capacitors are connected to the probes with respect to polarity. If the capacitance of the capacitor is more than 1 µF and it is in good condition, then after connecting the ohmmeter, the capacitor is charged, and the arrow of the device quickly deviates towards zero (and the deviation depends on the capacitance of the capacitor, the type of device and the voltage of the power source), then the arrow slowly returns to the “infinity” position.

If there is a leak, the ohmmeter shows a low resistance - hundreds and thousands of ohms - the value of which depends on the capacitance and type of capacitor. When a capacitor breaks down, its resistance will be near zero. When checking serviceable capacitors with a capacity of less than 1 µF, the instrument needle does not deviate, because the current and charging time of the capacitor are insignificant. When checking with an ohmmeter, it is impossible to determine the breakdown of the capacitor if it occurs at the operating voltage. In this case, you can check the capacitor with a megohmmeter at a device voltage that does not exceed the operating voltage of the capacitor. Medium capacitors (from 500 pF to 1 μF) can be checked using headphones and a current source connected in series to the terminals of the capacitor. If the capacitor is working properly, a click is heard in the headphones when the circuit closes. Low-capacity capacitors (up to 500 pF) are checked in a high-frequency current circuit. A capacitor is connected between the antenna and the receiver. If the volume does not decrease, then there are no broken leads.

How to check a transformer, inductor, inductor

The check begins with an external inspection, during which it is necessary to ensure that the frame, screen, and terminals are in good condition; in the correctness and reliability of connections of all parts of the coil; in the absence of visible wire breaks, short circuits, damage to insulation and coatings. Particular attention should be paid to areas of charring of the insulation, frame, blackening or melting of the fill. The most common cause of failure of transformers (and chokes) is their breakdown or short circuit of turns in the winding or broken leads. An open coil circuit or the presence of short circuits between windings isolated according to the circuit can be detected using any tester. But if the coil has a large inductance (i.e., consists of a large number of turns), then a digital multimeter in ohmmeter mode can deceive you (show an infinitely large resistance when there is still a circuit) - the digital multimeter is not intended for such measurements. In this case, an analog dial ohmmeter is more reliable. If there is a circuit being tested, this does not mean that everything is normal. You can make sure that there are no short circuits between the layers inside the winding, leading to overheating of the transformer, by the inductance value, comparing it with a similar product. When this is not possible, you can use another method based on the resonant properties of the circuit. From the tunable generator we apply a sinusoidal signal alternately to the windings through a separating capacitor and control the shape of the signal in the secondary winding.

If there are no interturn short circuits inside, then the signal shape should not differ from sinusoidal over the entire frequency range. We find the resonant frequency by the maximum voltage in the secondary circuit. Short-circuited turns in the coil lead to disruption of oscillations in the LC circuit at the resonant frequency. For transformers for different purposes, the operating frequency range is different - this must be taken into account when checking: - mains supply 40...60 Hz; - audio isolation 10...20000 Hz; - for a switching power supply and isolation.. 13... 100 kHz. Pulse transformers usually contain a small number of turns. If you manufacture them yourself, you can verify their performance by monitoring the transformation ratio of the windings. To do this, we connect the transformer winding with the largest number of turns to a sinusoidal signal generator at a frequency of 1 kHz. This frequency is not very high and all measuring voltmeters (digital and analogue) operate at it, at the same time it allows you to determine the transformation ratio with sufficient accuracy (they will be the same at higher operating frequencies). By measuring the voltage at the input and output of all other windings of the transformer, it is easy to calculate the corresponding transformation ratios.

How to check a diode, photodiode

Any pointer (analog) ohmmeter allows you to check the passage of current through a diode (or photodiode) in the forward direction - when the “+” of the tester is applied to the anode of the diode. Turning a working diode back on is equivalent to breaking the circuit. It will not be possible to check the transition with a digital device in ohmmeter mode. Therefore, most modern digital multimeters have a special mode for testing p-n junctions (it is marked with a diode on the mode switch). Such transitions are found not only in diodes, but also in photodiodes, LEDs, and transistors. In this mode, the digital camera works as a source of stable current of 1 mA (this current passes through a controlled circuit) - which is completely safe. When the controlled element is connected, the device shows the voltage at the open p-n junction in millivolts: for germanium 200...300 mV, and for silicon 550...700 mV. The measured value can be no more than 2000 mV. However, if the voltage on the multimeter probes is lower than the triggering of the diode, diode or selenium column, then direct resistance cannot be measured.

Checking the bipolar transistor

Some testers have built-in gain meters for low-power transistors. If you do not have such a device, then using a conventional tester in ohmmeter mode or a digital tester in diode testing mode, you can check the serviceability of the transistors. Testing bipolar transistors is based on the fact that they have two n-p junctions, so the transistor can be represented as two diodes, the common terminal of which is the base. For an n-p-n transistor, these two equivalent diodes are connected to the base by anodes, and for a p-n-p transistor, by cathodes. The transistor is good if both junctions are good.

To check, one multimeter probe is connected to the base of the transistor, and the second probe is alternately touched to the emitter and collector. Then swap the probes and repeat the measurement.

When testing the electrodes of some digital or power transistors, it should be taken into account that they may have protective diodes installed inside them between the emitter and the collector, as well as built-in resistors in the base circuit or between the base and emitter. Without knowing this, the element may be mistakenly mistaken for faulty.

radiostroi.ru

How to test a transistor with a multimeter in ohmmeter and hFE measurement mode

A transistor is a semiconductor device whose main purpose is to be used in circuits to amplify or generate signals, as well as for electronic switches.

Unlike a diode, a transistor has two pn junctions connected in series. Between the transitions there are zones with different conductivities (type “n” or type “p”), to which the terminals for connection are connected. The output from the middle zone is called the “base”, and from the extreme ones - the “collector” and “emitter”.

The difference between the “n” and “p” zones is that the first has free electrons, and the second has so-called “holes”. Physically, a "hole" means there is a lack of an electron in the crystal. Electrons, under the influence of the field created by a voltage source, move from minus to plus, and “holes” - vice versa. When regions with different conductivities are connected to each other, electrons and “holes” diffuse and a region called a p-n junction is formed at the boundary of the connection. Due to diffusion, the “n” region turns out to be positively charged, and the “p” region is negatively charged, and between regions with different conductivities, an own electric field arises, concentrated in the region of the p-n junction.

When the positive terminal of the source is connected to the “p” region, and the negative terminal to the “n” region, its electric field compensates for the p-n junction’s own field, and an electric current passes through it. When connected in reverse, the field from the power source is added to its own, increasing it. The junction is locked and no current passes through it.

The transistor contains two junctions: collector and emitter. If you connect the power source only between the collector and emitter, then no current will flow through it. One of the passages turns out to be locked. To open it, potential is applied to the base. As a result, a current arises in the collector-emitter section, which is hundreds of times greater than the base current. If the base current changes over time, then the emitter current exactly repeats it, but with a larger amplitude. This is what determines the reinforcing properties.

Depending on the combination of alternating conduction zones, p-n-p or n-p-n transistors are distinguished. P-n-p transistors open when the base potential is positive, and n-p-n transistors open when the base potential is negative.

Let's look at several ways to test a transistor with a multimeter.

Checking the transistor with an ohmmeter

Since the transistor contains two p-n junctions, their serviceability can be checked using the method used for testing semiconductor diodes. To do this, it can be thought of as the equivalent of a back-to-back connection of two semiconductor diodes.

The serviceability criteria for them are:

• Low (hundreds of Ohms) resistance when connecting a DC source in the forward direction;
• Infinitely high resistance when connecting a DC source in the reverse direction.

A multimeter or tester measures resistance using its own auxiliary power source - a battery. Its voltage is small, but it is enough to open the pn junction. By changing the polarity of connecting the probes from the multimeter to a working semiconductor diode, in one position we get a resistance of a hundred Ohms, and in the other - infinitely large.

A semiconductor diode is rejected if

• in both directions the device will show a break or zero;
• in the opposite direction, the device will show any significant resistance value, but not infinity;
• The device readings will be unstable.

When checking a transistor, six resistance measurements with a multimeter will be required:

• base-emitter direct;
• base-collector direct;
• base-emitter reverse;
• base-collector reverse;
• emitter-collector direct;
• emitter-collector reverse.

The criterion for serviceability when measuring the resistance of the collector-emitter section is an open circuit (infinity) in both directions.

Transistor Gain

There are three schemes for connecting a transistor to amplifier stages:

• with a common emitter;
• with a common collector;
• with a common base.

They all have their own characteristics, and the most common is the common emitter circuit. Any transistor is characterized by a parameter that determines its amplification properties - gain. It shows how many times the current at the output of the circuit will be greater than at the input. For each of the switching schemes there is its own coefficient, different for the same element.

The reference books give the coefficient h31e - the gain factor for a circuit with a common emitter.

How to Test a Transistor by Measuring Gain

One of the methods for checking the health of a transistor is to measure its gain h31e and compare it with the passport data. The reference books give the range in which the measured value can be for a given type of semiconductor device. If the measured value is within the range, then it is normal.

The gain is also measured to select components with the same parameters. This is necessary for building some amplifier and oscillator circuits.

To measure the h31e coefficient, the multimeter has a special measurement limit designated hFE. The letter F stands for “forward” (straight polarity), and the “E” stands for common emitter circuit.

To connect the transistor to the multimeter, a universal connector is installed on its front panel, the contacts of which are marked with the letters “EVSE”. According to this marking, the terminals of the transistor “emitter-base-collector” or “base-collector-emitter” are connected, depending on their location on a particular part. To determine the correct location of the pins, you will have to use a reference book, where you can also find out the gain factor.

Then we connect the transistor to the connector, selecting the measurement limit of the multimeter hFE. If its readings correspond to the reference values, the electronic component being tested is operational. If not, or the device shows something unintelligible, the transistor has failed.

Field-effect transistor

A field-effect transistor differs from a bipolar transistor in its operating principle. Inside the crystal plate of one conductivity (“p” or “n”), a section with a different conductivity, called a gate, is introduced in the middle. At the edges of the crystal, pins are connected, called source and drain. When the gate potential changes, the size of the current-carrying channel between the drain and the source and the current through it change.

The input resistance of the field-effect transistor is very high, and as a result it has a high voltage gain.

How to test a field effect transistor

Let's consider testing using the example of a field-effect transistor with an n-channel. The procedure will be as follows:

1. We switch the multimeter to diode testing mode.
2. We connect the positive terminal from the multimeter to the source, and the negative terminal to the drain. The device will show 0.5-0.7 V.
3. Change the polarity of the connection to the opposite. The device will show a break.
4. We open the transistor by connecting the negative wire to the source and touching the gate with the positive wire. Due to the existence of the input capacitance, the element remains open for some time; this property is used for testing.
5. We move the positive wire to the drain. The multimeter will show 0-800 mV.
6. Change the polarity of the connection. The device readings should not change.
7. We close the field-effect transistor: the positive wire to the source, the negative wire to the gate.
8. We repeat points 2 and 3, nothing should change.

voltland.ru

Is it possible to check a field-effect transistor with a multimeter?

This is a relatively new type of transistor, which is controlled not by electric current, as in bipolar transistors, but by electric voltage (field), as indicated by the English abbreviation MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor or metal-oxide-semiconductor field effect transistor). transistor), in Russian transcription this type is designated as MOS (metal-oxide-semiconductor) or MOS (metal-dielectric-semiconductor).

A distinctive design feature of field-effect transistors is an insulated gate (a terminal similar to the base of bipolar transistors); MOSFETs also have drain and source terminals, analogous to the collector and emitter of bipolar transistors.

There is an even more modern type of IGBT, in Russian transcription IGBT (insulated gate bipolar transistor), a hybrid type, where an MOS (MDS) transistor with an n-type junction controls the base of the bipolar one, and this allows you to take advantage of the advantages of both types: speed, almost like in the field, and a large electric current through the bipolar with a very small voltage drop across it when the gate is open, with a very high breakdown voltage and high input resistance.

Field devices are widely used in modern life, and if we talk about a purely household level, then these are all kinds of power supplies and voltage regulators from computer hardware and all kinds of electronic gadgets to other, simpler household appliances - washing machines, dishwashers, mixers, coffee grinders, vacuum cleaners , various illuminators and other auxiliary equipment. Of course, something from all this variety sometimes fails and there is a need to identify a specific malfunction. The very prevalence of this type of detail raises the question:

How to test a field-effect transistor with a multimeter?

Before any check of the field-effect transistor, you need to understand the purpose and marking of its terminals:

• G (gate) - gate, D (drain) - drain, S (source) - source

If there is no marking or it is not readable, you will have to find the product passport (dataship) indicating the purpose of each pin, and there may be not three, but more pins, this means that the pins are interconnected internally.

And you also need to prepare a multimeter: connect the red probe to the positive connector, respectively, the black one to the minus connector, switch the device to diode testing mode and touch the probes to each other, the multimeter will show “0” or “short circuit”, separate the probes, the multimeter will show “1” or “infinite circuit resistance” - the device is working. There is no need to talk about a working battery in a multimeter.

Connecting the multimeter probes is indicated for checking an n-channel field-effect transistor, the description of all tests is also for the n-channel type, but if you suddenly come across a rarer p-channel field-effect transistor, the probes must be swapped. It is clear that the first priority is to optimize the testing process so that you have to desolder and solder as few parts as possible, so you can see how to test a transistor without desoldering in this video:

Checking the field worker without desoldering

It is preliminary, it can help determine which part needs to be checked more precisely and, perhaps, replaced.

When checking the field-effect transistor, without unsoldering, be sure to disconnect the device being tested from the network and/or power supply, remove the batteries or batteries (if any) and begin testing.

1. Black probe on D, red on S, the multimeter reading is approximately 500 mV (millivolts) or more - most likely serviceable, a reading of 50 mV is suspicious, when the reading is less than 5 mV - most likely faulty.
2. Black is on D, and red is on G: a large potential difference (up to 1000 mV and even higher) - most likely serviceable, if the multimeter shows close to point 1, then this is suspicious, small numbers (50 mV or less), and close to the first point - most likely faulty.
3. Black on S, red on G: about 1000 mV and above - most likely serviceable, close to the first point - suspicious, less than 50 mV and coincides with previous readings - apparently the field-effect transistor is faulty.

Did the check show a preliminary malfunction on all three points? You need to desolder the part and proceed to the next step:

Checking a field-effect transistor with a multimeter

Includes preparing a multimeter (see above). It is imperative to remove static voltage from yourself and the accumulated charge from the field worker, otherwise you can simply “kill” a completely serviceable part. Static voltage can be removed from yourself using an antistatic cuff; the accumulated charge is removed by short-circuiting all terminals of the transistor.

First of all, you need to take into account that almost all field-effect transistors have a safety diode between the source and drain, so we start checking with these terminals.

1. Red probe on S (source), black on D (drain): multimeter readings around 500 mV or slightly higher - good, black probe on S, red on D, multimeter readings “1” or “infinite resistance” - shunt diode is working .
2. Black on S, red on G: multimeter reading “1” or “infinite resistance”, the norm, at the same time charged the gate with a positive charge, opened the transistor.
3. Without removing the black probe, we move the red probe to D, current flows through the open channel, the multimeter shows something (not “0” and not “1”), we swap the probes: the readings are approximately the same - the norm.
4. Red probe on D, black on G: multimeter reading “1” or “infinite resistance” is normal, at the same time we discharged the gate and closed the transistor.
5. The red one remains on D, the black probe remains on S, the multimeter reading “1” or “infinite resistance” is OK. We swap the probes, multimeter readings around 500 mV or higher are normal.

Conclusion from the test: there are no breakdowns between the electrodes (leads), the gate is triggered by a small (less than 5V) voltage on the multimeter probes, the transistor is working.

How to test a transistor without desoldering it from the circuit

Do-it-yourself electrical circuits in the house

Grounding schemes for a private house

Designation on the electrical diagram

Designation on the electrical diagram

Current stabilizer circuits

And industrial devices with LEDs. They are found almost everywhere today. They are also starting to use LEDs instead of old tubular fluorescent lamps, but we can keep silent about incandescent lamps. Due to the fact that there is a huge variety of diodes, to check them it will be useful to have a tester, or make one yourself.

Of course, some LEDs can be checked with a regular multimeter in dial mode. The LED should light up. But if it operates at a higher voltage than the multimeter outputs, the glow will be very weak or not at all.
For some white, yellow and blue LEDs, the voltage can reach 3.3V.

First of all, when testing an LED, you need to determine where its cathode is and where its anode is. Of course, this can be determined by examining the insides of the crystal, but this takes time, effort, nerves, and in general this is an unprofessional approach.

Among other things, the manufactured probe will help determine what operating voltage the LED has, and this is a very important parameter. And finally, the device will help you trivially determine the serviceability of the LED.

Device diagram
According to the author, the device circuit is very simple. The homemade product is an attachment that plugs into the socket of a multimeter.


Materials and tools for homemade work:
- connecting block from a “Krona” type battery;
- working battery (needed to power the probe);
- a miniature button without locking (a clock button from a phone, tablet, etc. is also suitable);
- one 1 kOhm resistor for 0.25 W;
- quick-release connector for transistors (socket with a pitch of 2.54 mm, a total of 3 contacts will be needed);
- material for creating a housing for the device (a plastic plate, etc. will do);
- four brass screws.

Homemade manufacturing process:

Step one. We prepare the necessary elements
First you need to prepare the contacts that will connect to the multimeter. The photo shows that the pins have threads, but it is best to get rid of them. The thread is needed only to screw the elements using nuts to the plastic body.

To attach the pins, you need to drill fourth holes in the plastic plate. Two are needed to install the connecting block through which the Krona battery is connected. And the second two are needed for mounting the contacts with which the device is connected to the multimeter.

To attach the microbutton and the connector for transistors, you will need to cut the board out of PCB.

Step two. Soldering the circuit
Now you need to solder the electronic parts, guided by the diagram presented above. You need to solder a microbutton, a transistor socket and a 1 kOhm 0.25 W resistor.

Step three. The final stage. Homemade assembly
Now the device is assembled into a common housing. The removed wires are connected to the power supply block for the Krona battery and to the plugs with which the probe is connected to the multimeter. On the PCB board near the connector, the author glued a circuit that allows you to avoid confusion when testing the LED. The red power wire is the “plus”, that is, the anode. Well, the black one with a minus sign is the cathode.

To test the LED, you need to plug it into the connector and connect the Krona battery to the socket. The multimeter now switches to voltage measurement mode in the range of 2-20V DC. If the diode is working and turned on correctly, it will light up.

As mentioned at the beginning, you can use a multimeter to determine the operating voltage of the LED, but if this is not necessary, a multimeter is not needed at all. That's all, the little helper is ready, now it will be much more pleasant and faster to assemble homemade products with LEDs or repair something.

Good day everyone, I would like to present a probe for transistors that will definitely show whether it is working or not, because it is more reliable than simply testing its terminals with an ohmmeter like diodes. The diagram itself is shown below.

Probe circuit

As we can see, this is an ordinary blocking generator. It starts up easily - there are very few parts and it is difficult to mix anything up during assembly. What we need to build the circuit:

1. Bread board
2. LED of any color
3. Momentary button
4. 1K resistor
5. Ferrite ring
6. Varnished wire
7. Socket for microcircuits

Assembly parts

Let's think about what we can pick up from where. You can make such a breadboard yourself or buy it; the easiest way is to assemble it with a canopy or on cardboard. The LED can be picked out from a lighter or from a Chinese toy. A button without locking can be picked from the same Chinese toy, or from any burnt-out household device with similar controls.

The resistor does not have to have a nominal value of 1K - it can deviate from the specified nominal value within 100R to 10K. A ferrite ring can be taken from an energy-saving lamp, and not necessarily a ring - you can also use ferrite transformers and ferrite rods, the number of turns is from 10 to 50 turns.

The wire is varnished, it is permissible to take almost any diameter from 0.5 to 0.9 mm, the number of turns is the same. You will learn how to connect the windings for proper operation during testing - if it doesn’t work, then simply swap the ends of the terminals. That's all, now a short video of the work.

Video of the tester working

There are many different circuits for testing transistors and measuring their parameters. But in practice, most often you just need to quickly make sure that the transistor in the circuit is working, without going into the intricacies of its current-voltage characteristics.

Below are two simple diagrams of such probes. They have a minimum of parts and do not require any special adjustment. At the same time, with their help you can easily and quickly test almost any transistor (except field-effect ones), both low-power and high-power, without removing it from the circuit. Also, using these circuits, you can experimentally determine the pinout of the transistor, the location of its terminals, if the transistor is unknown to you and there is no reference information on it. The currents through the transistor being tested in these circuits are very small, so even if you “reverse the polarity,” you will not damage the transistor.

The first circuit is assembled using a low-power transformer Tr1 (this can be found in almost any old pocket or portable transistor receiver, for example, Neva, Chaika, Sokol).

Such transformers are called transition transformers and serve to match the amplification stages in the receiver. The secondary winding of the transformer (it has a middle terminal) must be reduced to 150 - 200 turns.

The meter can be assembled in a suitable small-sized housing. The Krona type battery is located in the housing and is connected through the appropriate connector. Switch S1 - type “P2-K” or any other with two groups of contacts for switching. A capacitor can be taken with a capacity of 0.01 to 0.1 µF, and the tonality of the sound will change. Measuring probes “e”, “b”, “k” are made from pieces of wire of different colors, and it is convenient to make sure that the first letter of the wire color matches the letter of the transistor output. For example: TO red - " TO collector", B white - " B aza", E Mitter – any other color (because there is no color starting with the letter “E”!). You need to solder small pieces of copper wire to the ends of the wires as tips. The probe can be assembled by mounted mounting by soldering a resistor and capacitor directly to the contacts of the switch and transformer.

If the transistor being tested is in good working order in the telephone capsule connected to the second winding of the transformer, a sound will be heard. It is necessary to use a high-impedance sound emitter (such as "DEMSH", for example), since the volume of its sound is sufficient for good audibility at a distance, so it can be located in the device body, and not taken outside. Low-impedance headphones and speakers will bypass the secondary winding of the transformer and the device may not work. You can turn on a telephone capsule as an emitter (take it out of an old handset. Although a new one will also work). If there is no suitable sound emitter with high resistance at all, then you can use an LED by connecting it instead of a capsule through an additional resistance (select the resistance taking into account the output voltage on the transformer so that its brightness is sufficient), then if the transistor is working properly, the LED will light up.

The second probe circuit is transformerless. The device and principle of operation are similar to the previous diagram

I have been using a similar circuit for many years and is capable of testing any transistors. Transistors of the old MP-40 type were used as T1 and T2, which can be replaced with any of this series (MP-39, -40, -41, -42). These are germanium transistors, the opening current of which is noticeably lower than that of silicon ones (such as KT-361, KT-3107, etc.) and when testing transistors without desoldering them from the circuit, no problems arise (the effect on the active elements of the circuit being tested is minimal). It is quite possible that modern silicon transistors will be suitable, but I personally have not tested this option in practice.

The battery in this circuit should be turn off after work, otherwise it will be discharged through the open junctions of transistors T1 and T2.

As already mentioned at the beginning, with the help of these probes you can determine the pin markings and conductivity type (p – n – p / n – p – n) of unknown transistors. To do this, the transistor leads must be alternately connected to the probe probes in different combinations and at different positions of switch S1 until a sound signal appears.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
	Option 1.
	Capacitor	0.047 µF	1			To notepad
	Resistor	22 kOhm	1			To notepad
	Sound emitter	DEMSH	1			To notepad
Tr1	Transformer		1	From an old transistor radio		To notepad
S1	Switch		1			To notepad
	Battery	9 V	1			To notepad
	Option 2.
T1, T2	Transistor	MP-40	2	Possibly others		To notepad
R1, R4	Resistor	39 kOhm	2			To notepad
R2, R3	Resistor	1 kOhm	2